1. Field of the Invention
This invention relates to a print head of a printer used with a facsimile machine, wordprocessor, or the like.
2. Description of the Related Art
Hitherto, thermal printers for printing by heating the heating elements for transferring ink of an ink ribbon to paper or developing color on thermosensible paper have been known. Particularly, the thermal printers can be easily miniaturized and are used with various machines such as facsimile machines and wordprocessors.
The thermal printer has heating elements for one line and heats them in response to print data for one line of printing. Thus, the thermal printer has a shift register which stores 1-line of print data which is set in the register. The shift register is formed with driver ICs for every 32 or 64 bits. The driver ICs are connected in series conforming to the number of dots of a thermal print head to enable printing on one line. That is, each driver IC has one data input pin and one data output pin and the data output pin of one driver IC is connected to the data input pin of another driver IC, thereby increasing the number of bits of the shift register.
For example, a thermal head for a facsimile machine to print on paper of A4 size provides 1728 dots if the dot density is eight dots/mm, and comprises 27 64-bit driver ICs connected in series; to print on paper of B4 size, the thermal head provides 2048 dots and comprises 32 64-bit driver ICs connected in series.
Although a plurality of IC drivers are thus connected in series to increase the number of bits, preferably the number of bits of one driver IC should be increased for reducing costs. In recent years, the integration degree of IC has advanced with the progress of the IC manufacturing technologies, and it is easy to increase the number of bits of one driver IC; for example, it is possible to increase the number of bits to 96 or 128.
However, if the number of bits of one driver IC is increased, flexibility in combination will be less, and the number of dots of a thermal head may not match the total number of bits of driver ICs. For example, to use 96-bit driver ICs to provide 2048 dots, ##EQU1## thus, if 21 driver ICs are connected in series, it is 32 bits short; if 22 driver ICs are connected in series, there are 64 bits too many.
Then, 22 driver ICs are connected in series and the last 64-bit register portion is not used. However, in the configuration, output of the output pin of the last driver IC contains data in the unused register portion, and does not correspond to print data. Output data of driver ICs may be noted depending on print head application, in which case the print head is not applicable.